Melissa Call-Projects

Melissa Call-Projects

Projects

Melissa Call-Projects

The T cell antigen receptor (TCR) recognizes peptide fragments bound to major histocompatibility complex (MHC) proteins, activating T cells to kill target cells and/or secrete soluble factors. While the structural determinants of ligand discrimination are well studied, the mechanism by which receptor engagement outside the cell is sensed by signalling molecules inside the cell is still an open question. We are combining disulphide mapping and solution NMR techniques to determine how the eight-subunit receptor complex is arranged within the membrane and how transmembrane structure and dynamics relate to receptor activation.

Team member: Logesvaran Krshnan

DAP12-dependent NK cell receptor assembly and function

Natural killer (NK) cells are lymphocytes that eliminate cells exhibiting dysregulated MHC or otherwise altered cell-surface phenotypes, often due to viral infection or oncogenic transformation. A vast array of receptors governs the balance between NK cell cytotoxicity and quiescence, and many of the activating receptors depend on a homodimeric signalling module called DAP12 to supply cytosolic links to intracellular biochemical cascades. This project applies solution NMR and, more recently, lipidic cubic phase (LCP) crystallography techniques to examine the transmembrane structures adopted by DAP12 during assembly with “client” receptors.

The levels of peptide:MHC complexes and other immunologically relevant proteins available at the cell surface can be modulated by regulatory proteins of the Membrane-Associated RING-CH (MARCH) family. MARCHs are integral membrane proteins with alpha-helical TM domains and cytosolic ubiquitin ligase domains. We use cellular biochemical and flow-cytometry based functional assays combined with solution NMR and lipidic cubic phase (LCP) crystallography techniques to study how MARCH proteins trap substrates through interactions with their TM domains. The major aim of this project is to identify what structural motifs govern substrate identification and thereby identify new substrates and molecular pathways that are MARCH-regulated.